Electron discharge devices



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Apnl 19, 1960 E. c. DENCH 2,933,638

ELECTRON DISCHARGE DEVICES Filed July 19, 1956 2 Sheets-Sheet 2 67 .ILE 92265 92a Ammmex 6/ l i I L 27 5%- vlig/? -Izo United' States PatentfO ELECTRON DISCHARGE DEVICES Edward C. Dench, Needham, Masa, assigner to Raytheon Company, a corporation of Delaware Application July 19, 1956, Serial No. 598,816

Claims. (Cl. S15-3.5)

This invention relates to electron discharge devices of the traveling wave type, and more particularly, to means for frequency-modulating such devices with low power.

in electron devices of the traveling wave type, wherein signal waves traveling along a network interact with electrons moving along paths adjacent to the network to produce oscillation, the frequency of oscillation may be changed by changing the potential applied between the network and the cathode. ln the case where there is a transverse magnetic eld, the frequency is determined by the electron velocity of the beam, which, in turn, is dctermined by the formula:

Va-r- V, E,

da. e (l) in which Va is the voltage of the anode or delay line with reference to the cathode, Vs is the voltage of the sole electrode arranged parallel to the anode, B is the magnitude of the magnetic eld in gauss, d is the distance between the sole and the anode, and E,l is the electrical field. It can be seen that the frequency of operation could be changed by varying any of the values Va, VS, B, or d. However, d cannotbe readily varied once determined. B could be an electromagnet and its strength varied by varying the current through its windings. However, stability and other considerations usually dictate a permanent magnet. Because of other design considerations, the sole potential Vs can only be varied over a small range. Thus the frequency of oscillation of traveling wave oscillators is usually determined by the potential on the delay line with respect to the cathode. However, there is considerable beam current carried by the anode that complicates the design of a modulator -for this voltage, particularly at higher powers where this anode current and voltage must be high. In certain types of traveling wave tubes, the anode structure is Vformed of two sets of elements. 'Y

This type of construction is made use of by thev in- Average electron velocity:

Vvention .to overcome the above-mentioned difliculties.

The two sets of elements may be mounted so that, while all the elements of each set lare connected together, each set is connected to a separate potential. The greatest current will flow to the set of elements at the highest positive potential with respect to the cathode, yet the potentials on both sets of elements will determine the average electrical field EB as follows:

current, thus simplifying its design.v This effect canY be enhanced if the set of elements at the lesser potential are also positioned further away from the electron stream than the elements at the higher potential.

Other and further objects and features of this invention will be apparent as the description progresses, reference being had to the accompanying drawing wherein:

Fig.'1 is a vertical section View taken centrally of one embodiment of a backward-wave traveling-wave oscillator incorporating the invention;

Fig. 2 is a horizontal section taken along the line 2-2 of Fig. 1;

Fig. 3 is a schematic diagram of the delay line of the invention;

Fig. 4 is a schematic diagram of the circuit used with the tube of the invention;

Fig. 5 is a schematic diagram of the circuit used with a modied embodiment of the tube of the invention;

Fig. 6 is a vertical cross section of a circular embodiment of the invention showing the associated circuit schematically; and

Fig. 7 is an enlarged detail of Fig. 6 showing a way of mounting the two sets of anode elements.

In Figs. 1 and 2, the invention is illustrated as incorporated into a linear, interdigital, backward-wave, traveling-wave amplifier with a transverse magnetic Vfield. The reference numeral 10 designates the envelope of the tube comprising top and bottom plates 1li and 12, iside plates 13 and 14, and end plates 15 and i6, which are hermetically sealed together to form an oblong boar. Positioned inside the envelope 10, rigidly attached to the top plate 11 and extending the length thereof, between end plates 15 and 16, are a pair of spaced parallel anode support members 17 and 1S, preferably of metal. Each support member 17 or 18 has attached thereto arset of anode elements 21 and 2i), respectively, which extend toward the opposite support member 17 or 1S in the form of fingers that overlap to form an interdigital or folded waveguide type of anode network structure. These lingers 2t) and 21 are spaced from the top plate 11 and thetingers of opposing sets are spaced from each other. One set 21 of such lingers and its associated support 17 are insulated from the envelope 1.6 by means of pieces of insulating material 22. e

' Positioned somewhat beyond one end and below the network of lingers 2li and 21 is a cathode structure 23 comprising a cathode support member 24, which may be, for example, an annular cylindrical member which extends downward through an opening in the lower plate 12, spaced therefrom and insulatcdly sealed thereto by means of an insulating seal 25 and a cylindrical mem- Which is, in turn, sealed into the aperture in the bottom plate 12 through which support plate Ymember 24 passes. An indirectly heated cathode 27 is shown, by way of example, as being rigidly attached to the inner end of support member 24. Cathode 27 comprises a boxlike structure containing a heater wire 28, one end of the heater wire being connected to the cathode 27, and the other end thereof being connected to a lead-in member 30 extending outward through support cylinder 24 and spaced therefrom, and insulatedly sealed to the lower end of the support cylinder by an insulating seal 31. The surface of the cathode 27, which is presented to the plane containing lingers 20 and 21, is coated with an elcctron-emissive material. Other types of cathode construction and other means for heating such cathodes may be used.

A conductive block 32 is attached to the inside of upper plate 11, directly opposite the electron-emissive surface of the cathode 27, for the purpose of correctly shaping the electron stream which, upon the heating of cathode 27, emanates. from the electron-emissive coating` and is directed along paths adjacent the lower surfaces of fingers 20 and 21 under the inuence of an electrostatic field, produced between said fingers, and a sole 33 positioned below lingers 26 and 21 and supported on leadin supports 34, extending out through the bottom plate 12 and insulated therefrom. The electron stream is also under the iniiuence of a magnetic iield produced transverse to the electrostatic field by means of magnetic pole pieces 35, forming part of a magnet, the bulk of which is not shown. The envelope 1G Vis maintained.` positive with respect to the sole electrode 33, and the potential on the cathode'structure 23 is .adjusted so that electrons emanating fromk the cathode surface 27 will, with the proper polarity of magnetic eld produced between pole pieces 35, travel down the Yspace between the fingers. 20 Vand 21 and the sole 33 (as best seen in Fig54), whereby signals traveling alongY the network of fingers 20ja r1d 21 will interact with the said electrons causing signal amplitude buildup, and in this case, oscillations.

Attached to the anode finger element 20 nearest the cathode structure 23 is a signal output lead 36, which extends outwardly through an aperture in the top plate 11, and forms the central conductor of the coaxial line 37, whose outer conductor 38 is sealed to the aperture in the top plate 11 through which member 36 passes. Member 36 is insulatedly sealed to outer conductor 38 by means of a ceramic seal inside of a coaxial line 37, not shown. Elements 36 and 38 form a signal output coupling structure by which high-frequency energy is extracted from the anode network and fed to any desired load. A coupling structure 40 is connected to the anode fingers 21, isolated by the insulators 22, in order to apply to these lingers a potential independent of that supplied to the set of anode lingers 20.

It can be best seen in the schematic diagram of Fig. 3 how the sets of lingers 21, formed on anode member 17, can be isolated from the fingers 29, formed on the anode member 18, by means of insulators 41, corresponding to the insulators 22 of Fig. 1. With this arrangement the lingers 20 can be connected to a source of fixedV anode potential and to the radio frequency energy output coupler. The isolated lingers 21 can be connected to a source of potentialnegative with respect to the source associated with the lingers 20.

This structure can be used in a frequency-modulated oscillator, as shown schematically in Fig. 4, in which the cathode is designated by the numeral 27 and is maintained at a potential negative with respect to the anode elements 29 by means of the source of potential 52. Anode elements 21 are also maintained at a potential positive with respect to the cathode 27 by means of a variable source of potential 54 that can include the source of modulating signals. This potential is different from that provided by the source 52 to the anode elements 20; preferably it supplies a lower potential so that the anode elements 2l are at a negative potential with respect to the anode elements 20. A sole electrode 33 is provided parallel to, and spaced from, the anode elements 20 and 21. This sole electrode is maintained at a potential negative with respect to the cathode 27 by means of a source of potential 56. The result is a beam of electrons moving from the cathode 27 to the anode elements 29 and 21 indicated by the dotted line 57. The greater portion of these electrons go to the anode elements 20, as shown by the lines 58, dueto their greater positive potential with respect to the cathode 27. However, in certain circumstances the tube mayact as a negative resistance, in which case the greater ow of current will go to the anode elements at lower potential with respect Vot the cathode. rfhe essential point is that the sets of fingers be isolated, and that the anode elements receiving the least, preferably zero, current have the modulating voltage applied to them so that the modulation equipment need carry only a minimum current and Yyet vary the effective anode-cathode voltage over arelatively wide range, and, hence, the frequency also, over a relatively wide range.

The anode elements 21 will draw less current at the same potential relative to the anode elements 20 if they are withdrawn further from the stream 57 of electrons and the surface of the sole 33. This construction is indicated in the schematic diagram of Fig. 5. This diagram is the same as Fig.`4, except that the group of elements 21a'correspondingto elements 21 of Fig. 4 are set further back from the electron beam 57 than the elements 21 ofFig. 4. `In this way the construction of the inventionicanV be made more effective.

The principle of the invention 'can be applied .to the circular type ofvtraveling wave tube -in the manner shown in Figs. 6 and 7, in which the reference numeral 60 designates a cylindrical envelope for the tube, comprising an annular outer wall 61, and top-62-and-bottom-63- plates joined to form a vacuum-tight envelope. The envelope includes a periodic slow-wave energy-propagating structure 64 mounted on the inner surface of the annular Wall 61. It a1so `includes a sole electrode 65, a lead-in assembly 66, an output coupling means 67, an electron gun assembly 68, including at least a cathode 70 'and a heater 71, and a transverse magnetic field-producing means, preferably a permanent magnet wtih pole pieces 72 and 73 which are illustrated in Fig. 6.

The delay line 64 is composed of two interleaved sets of fingers 74 and 75, which extend from oppositely disposed annular members 76 and 77, respectively. Members 76 and `77 are secured to the shoulderY 78 formed on the inner'surface of the annular wall 61. The annular member 77 is made of`insulating material, or insulatedly mounted on the shoulder 78. Provision is made to connect the fingers 75 to a source of fixed potential 80 and to a source of modulating potential 81 by means of a conductor 82 passing through an insulated bushing 83. n

The lead-in assembly 66 includes an electrically-conduetive cylindrical sleeve 84 inserted in an aperture in a cover plate 62 and securely attached thereto. A section of glass tubing 85 serves to mechanically and insulatedly connect metal sleeve 84 and a second metal sleeve 86. The outer end of the sleeve 86 is provided with a glass bead 87. The assembly 66 also includes an elongated electrically-conductive hollow supporting cylinder 88 which serves as the main support for the sole 65; One end of the cylinder 88`is fastened to the periphery of the aperture 90 in the sole.` The other end of the cylinder 88 contains an outwardly-flared portion 88a which is connected to the inner surface of the sleeve 86. The necessary leads for the electron'gun are fed through supporting cylinder 88 and are insulatedly supported therefrom and from-one another by glass beads 91.

A coaxial output coupling means 67 Is sealed in an openingin a wall 61 of the envelope 60 and are impedance-matched to the anode delay network 64. The inner conductor 67a of the coaxial output coupling means 67 is connected to a inger'at or adjacent one end ofthe set 74 of the periodic anode delay network` 64.

The electron `gunassembly 68 includes in addition the cathode 7G and heater 71, a pair of annular beam-forming plates or electrodes 92 supported from the bottom plate 63 by rigid posts 92a. The cathode 70 is shown as an annular iiat ring, one surface of which is coated with an electron-emissive material. The cathode shown is arranged coextensive with the annular interaction space 93 between the anode delay network 64 and the sole 65.

Cathode 70 is supported from the bottom plate 63 by` means of several blocks 94 of electrically-insulating material which are secured to the cathode and provided with openingsr95 to permit the passage of, and to atord support to, the heater filament 71 which is disposedadjacent the cahtode on the side opposite the emitting surface.

A cathode lead 96 Vis Vconnected at some point on thecathode 70 .and is broughtY out through the tubular supportingV cylinder 84 to the outside of theenvelope. One end of the heater 71 is connected to the cathode, and the other end is attached to a heater lead 97, passing through the cylinder 84 to the outside of the tube. The beam-forming plates 92 are interconnected by a jumper 100. A lead 101 is connected to one of these beam-forming plates and is brought out from the tube through cylinder 84.

A suitable electrical field between the cathode 70 and the first set of anode members 74 is obtained by .means of a unidirectional voltage from a source 102 through the conductor 96 and the metal envelope 60 which is electrically connected to the first Vset of anode members 74. The sole 65 is biased negatively with respect to the cathode 70 by means of the source of negative potential 103 connected between the conductor 96 and the sleeve 88 that is electrically and vmechanically connected to the sole 65. The director plates 92 are biased positively with respect to the cathode 70 by means of the source of positive potential 104 through conductor 101. The filament 71 is connected across the source of potential 105 by means of connectors 96 and 97 and the cathode 70. The isolated section 75 of the delay line is biased negative with respect to the iirst section of the delay line 75 bymeans of a tap 106 on the source 102, to which it is connected through a source of modulating signal 81 and the conductor 82. This construction is a modification of that shown in Figs. through 8 of the copending application of the applicant, Serial No. 575,113, led March 30, 1956, now U.S. Patent No. 2,865,004, issued December 16, 1958, where certain common features of the construction are more fully disclosed.

Other configurations of both the linear and circular delay line may be used so long as the delay line comprises two parts to which separate potentials may be applied and the tube may be of either the M type, having transverse electric and magnetic fields, or of the O type, having electrical fields only. Both of the tubes may be adapted for backward or forward wave operation.

This invention is not limited to the particular details of construction, materials and processes described, as

many equivalents will suggest themselves to those skilled in the art. t is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A traveling wave electron discharge device comprising a periodic slow wave energy-propagating network for transmitting electromagnetic Wave energy formed in two sections electrically insulated from each other and each section disposed about a separate arc, means for maintaining the two sections of said network at different unidirectional potentials, an electrode spaced from and substantially'coextensive with said periodic network, said network and said electrode at least partially defining an interaction space therebetween, and an electron source for injecting a beam of electrons into said interaction space in energy-interacting relationship with said wave energy.

2. A traveling wave electron discharge device comprising a periodic slow wave energy-propagating network for transmitting electromagnetic wave energy formed in two sections electrically insulated from each other and each section disposed about a separate arc, means for maintaining the two sections of said network at different unidirectional potentials, an electrode spaced from and substantially coextensive with said periodic network, said network and said electrode at least partially dening an interaction space therebetween, and an electron source for injecting a beam of electrons into said interaction space in energy-interacting relationship with said wave energy, said injecting means including means for producing mutually transverse electric and magnetic fields in the region of said interaction space and substantially perpendicular to said'ibeam of .electronsin said interaction space.

.3. A traveling wave electron discharge device comprising a periodic slow wave energy-propagating network for transmitting electromagnetic wave energy formed in two sections electrically insulated from each other and each section disposed about `a separate arc, means for maintaining the two sections of said network at dilerent unidirectional potentials, an electrode spaced from and substantially coextensive with said periodic network, said network` and said electrode at least partially defining an interaction space therebetween, an electron source for injecting a beam of electrons into said interaction space in energy-interacting relationship with said wave energy, and an output coupling vmeans at'the electron source end of said network.

4. A traveling wave electron discharge `device comprising a periodic lslow wave energy-propagating network for transmitting electromagnetic wave energy formed in two sections electrically insulated from each other and each section disposed about a separate arc, means for maintaining the two sections of said network at different unidirectional potentials, an electrode spaced from and substantially coextensive with said periodic network, said network and said electrode at least partially defining an interaction space therebetween, an electron source for injecting a beam of electrons into said interaction space in energy-interactingrelationship with said wave energy, said injecting means including means for producing mutually transverse electric and magnetic fields in the region of said interaction space and substantially perpendicular to said beam of electrons in said interaction space, and an output coupling means at the electron source end of said network.

5. A variabie-frequency oscillator circuit comprising a traveling wave electron device including cathode means for projecting a beam of electrons along a substantially regular path, a main anode structure on one side of said path and having a plurality of spaced parallel projections thereon with corresponding elements of said projections defining a first substantially regular surface, an auxiliary anode structure on said one side of said path and having a plurality of spaced parallel projections thereon corresponding elements of which dene a second substantially regular surface, an additional electrode on the side of said path opposite to said one side and having a substantially continuous surface parallel to the spaced projections of said first and second surfaces, and means connected to said main anode for providing an output connection for a load circuit, the projections of each of said anode structures being interdigitated with the projections of the other of said anode structures, circuit means interconnecting said main anode land said cathode means for maintaining the former at a potential positive with respect to the latter, circuit means interconnecting said auxiliary anode and said cathode for normally maintaining the former at a potential positive with respect to the latter but lessuthan that of said main anode, circuit means interconnecting said additional electrode and said cathode for normally maintaining the former at a potential negative with respect to the latter, and means for varying the potential applied between said auxiliary anode and said cathode means, whereby the frequency of the output provided at said output connection means may be varied in accordance with the variable potential applied to said auxiliary anode.

6. A variable-frequency electrical oscillator circuit in accordance with claim 5, wherein said first and second surfaces comprise a single surface.

7. A variable-frequency electrical oscillator circuit in accordance with claim 5, wherein the distance between said electron beam and said second surface is greater than the distance between said electron beam and said first surface, whereby current flow in the circuit connected to said auxiliary anode is significantly less than that in the circuit connected to said main anode. j g8. A variable-frequency electrical oscillator circuit, .comprising av traveling Wave electron discharge device having acathode, means for projecting a beam of electrons along a substantially linear path, a main anode vstructure oi substantially planar form on one side of Vsaid path, an auxiliary. anode structure of substantially planar form. on. said one side Yof saidV path and substantially parallelwithi said main anode,'an additionl electrode on thevside of said .path opposite tosaidone side and having asubstantially.continuoussurface parallel with said first andsecond surfaces, and Emeans connected to said main anode. for providingfan output Vconnection for a loadcircuit,; each, of said anode structures: having a .plurality of parallel projections extending in the plane of such anode and: interdigitatedwith 'the projections ofthe other of .saidanode structures, circuit means interconnecting said main anode'and said cathode means Vfor maintaining the former at a potential positive with respect to the latter, circuit means interconnecting said auxiliary anode and said cathode means for normally maintaining the former at a'potential positive with respect to the latter but less -nected to vsaid auxiliary anode is significantly less than tliatinzthe circuit connected tosaid mainfanodef i Y' "References Cited in theme of this 'patent v- UNITED STATES PATErr'rs:A 

